1. Field of the Invention
This invention relates generally to an internal connector for use with coiled tubing connector and a method by which coiled tubing is secured to the top of a downhole tool string used in the drilling and servicing of oil and gas wells.
2. Background of the Art
Increasingly, the drilling of oil and gas wells is done with boreholes that are deviated from the vertical. While such deviated drilling can be performed using a drillstring comprising sections of jointed drill pipe, in many instances, the drilling is performed by using a coiled tubing (CT) that conveys mud to a downhole drilling motor that drives a drillbit for the actual drilling. CTs are also used in subsequent logging and servicing of the borehole.
Tools so far developed for connecting and disconnecting the CT, which is not threaded, to downhole motors and tool strings suffer from many disadvantages, including poor resistance to rotation, inadequate strength, poor serviceability and general unreliability. U.S. Pat. No. 5,452,923 discloses a CT connector for addressing some of these problems. The device disclosed in the ""923 patent uses two tubular housings coupled together with a slip to anchor the CT and provide means for transmitting torque.
Typically, several thousand feet of tubing is coiled onto a large reel. The reel is mounted on a truck or skid. A CT injector head is mounted axially above the wellhead and the CT is fed to the injector for insertion into the well. The CT is plastically deformed as it is payed out from the reel and over a gooseneck guide which positions the CT along the axis of the wellbore and the injector drive mechanism.
Tools used with CT for production typically include one or more packer elements that act to isolate certain portions of the wellbore from each other. Such tools may be of any length but, for instance, for treatment of a particular interval in the wellbore, the tool must incorporate packer elements that, when positioned in the wellbore, effectively straddle and isolate that portion of the wellbore from the remaining portions, both above and below the zone of interest. Adding to the length of the tool string is the length of a coupling device for connecting the tool string to the CT. The coupling device, in addition to coupling the tool to the CT, also must be able to transmit torque, be detachable, and have valves therein to be able to close off any back-pressure from the well. These tools cannot be plastically deformed to pass around the reel or the gooseneck. In order to overcome this difficulty, it has been common prior practice to mount the tool in what is effectively an extension of the well casing above the wellhead and positioning the injector drive mechanism on top of this pressurized cylindrical enclosure.
Where the extra height above the wellhead is not available, the tool string is made up with a wireline lubricator and inserted into the borehole. During this insertion process, care has to be taken to maintain a pressure seal and avoid a blow-out. The wireline connector is replaced with the CT inserted from a suitable injection device. This extra step is time consuming and also has safety problems associated with it.
The present invention is an internal CT bottom hole assembly (IBHA) developed for applications where the CT is too large to use a conventional connector that attaches to the outside of the CT. It is also designed to eliminate, in some applications, the need for deploying the tool string by a pressure device conveyed on a wireline. Conventional connectors (either slip- or set screw-type), attached to the outside of the CT, may be larger than the tool string components being run. This can be a problem when running the tool string through small restrictions in the production tubing.
Since the IBHA fits inside the CT, there is no increase in diameter beyond that of the CT. This allows many operations to be completed with larger CT strings than would have been possible in the past. This is important in applications requiring maximum CT flow rate (e.g., acidizing) or tensile capacities (e.g. fishing) being done through tubing.
The IBHA includes a back pressure valve and a disconnect device. Having these two devices internal to the CT reduces the overall tool length requirements for inserting the CT into the borehole by 3-4xe2x80x2. This reduction in overall tool length is sufficient in many applications to eliminate the need for wireline pressure deployment of the tool string.